The stormy weather made an exit from the Waikato providing a clear morning to kick off the opening day of the 46th National Agricultural Fieldays at Mystery Creek.

Rain may have settled in during yesterday afternoon but Fieldays chief executive Jon Calder said he was happy with the number of people at the event on day one.

"Given the weather we had overnight, we're really happy with the way things have started out," Calder said.

"When we actually opened the gates we had semi-clear sky overhead and no rain, which was a bonus. Despite the odd shower, the day's been pretty good.

"We had about 22,000 [people] on site at midday, so it will probably be slightly down on what we were expecting compared with last year's number but, hey, given the weather we've had, probably to be expected."

Calder said 37 countries, including China, were represented by international visitors this year.

Site managers were making the best of the first day of the event, which concludes on Saturday.

Swanndri production manager Allan Brown said business on their site had been steady and he was reasonably happy with the traffic that had come through.

"Compared with last year it's quieter and if you look outside, it's quieter partly because apparently there are a lot of road closures too.

"It's been steady, and I would say it's about 70 per cent of where it was on the first day last year."

Brown was confident numbers would pick up through to Saturday once the weather settled.

Milk Bar's Brian Whyte also said site traffic was down but sales were about the same.

He believed genuine buyers had turned up at Fieldays while the weather kept the "lookers" away.

Farmers he had talked to on site were feeling very upbeat, he said.

Oringi Ltd's Chris Bousfield also thought more people would come in over the next couple of days.

"I wouldn't have come to the Fieldays based on last night's forecast, so you can't really blame people. They just postponed it for the day."

Police gave a warning for drivers to be careful on the roads around the site, with more traffic than usual in the area.

Xero New Zealand was upbeat about attendance. The first-time exhibitors and premier feature partner were "crazy busy" all day, marketing head Tarryn Brent said.

Brent said the company had been overwhelmed with interest in their farming in the cloud programme.

The event was officially opened by Prime Minister John Key, who said the farming industry was becoming "increasingly hi-tech".

Key said $38 billion per year was generated by agriculture in New Zealand and the country should be "100 per cent committed to the agricultural industry and 100 per cent committed to free trade".

The theme for the premier feature is managing resources for a competitive advantage and visitors flocked to the premier pavilion to see how the New Zealand agricultural sector can maintain its place as one of the world's best agricultural producers.

AT A GLANCE

Fieldays visitors should expect showers, easterly winds today, 15 degrees Celsius. Tomorrow and Saturday are forecast to be fine but gumboots are recommended.